I use a silver coloured Parker ballpoint, and every day when I leave work I hide it as coppers are awful magpies and I've already had one 'liberated'. (Or I lost it... we'll never know!) I started off using any old black biro but people will say "Can I just borrow your pen?" then you never see it again. Now I always carry my nice silver one and one for lending to useless bobbies with no pens!
I am only allowed to use black ink at work, the other day I had to sign my name in blue ink and it felt really odd. I don't really use blue at home now either. Institutionalised, much?!